1. Field of the Invention
The present invention relates to a method and apparatus for measuring decreasing thickness of the refractory lining of a high pressure, high temperature, water cooled reactor wall using a pulse-echo ultrasonic probe while the reactor is in operation.
2. State of the Art
A variety of methods are known to monitor corrosion of reactor walls. U.S. Pat. No. 3,056,248 discloses a scale and corrosion-measuring device and method extending into an environment and generating different frequencies of ultrasonic waves whose differences serve as a function of the corrosivity of the environment. U.S. Pat. No. 3,236,096 discloses an electrical gauge for sensing the amount of erosion of a solid material. U.S. Pat. No. 4,269,397 discloses a method of measuring the thickness of a refractory in a metallurgical apparatus by using timed pulses generated by a monitoring device in a critical wear area of the apparatus which then appears on a display as a straight line indicative of the thickness of the refractory. U.S. Pat. No. 4,510,793 discloses a process for monitoring the wear of a refractory lining by using an ultrasonic probe which is placed against the head of the ceramic bar which wears at the same rate as the refractory lining; its length is a measure of the remaining wall thickness at any time. U.S. Pat. No. 4,539,846 discloses an ultrasonic corrosion monitor for in situ measurement of corrosion of a monitoring zone using a probe placed in the corrosive environment where it is corroded; the ultrasonic probe also comprises thermocouples to allow temperature measurements to be made to adjust the measured time intervals to fixed temperature changes in the monitoring zone of the probe. However, none of these devices and methods is useful in a high pressure, high temperature, water cooled reactor during its operation where high temperaures, high pressures and corrosive amounts of hot gases, unburned fuel particles and slags provide a highly aggressive environment deleterious to refractory linings. The refractory lining used in such reactors requires (1) low solubility in slag and high resistance to abrasion by slag or unburned fuel particles; (2) high density to minimize slag penetration; (3) high thermal shock resistance, high strength and high volume stability during use in a gas environment and, particularly, (4) high thermal conductivity to allow more efficient heat extraction from the refractory/slag interface.
The objectives of the present invention include a method and apparatus to measure the decreasing thickness of the refractory lining in a high pressure, high temperature, water cooled reactor membrane wall during the operation thereof under aggressive environmental conditions as an indicator of possible erosion of the lining and wall studs, and to measure the temperature gradient across the refractory lining in a reactor to allow for compensation of error in the probe length caused by thermal expansion or any change in the properties of the materials due to temperature of the reactor and the environment.